TH2.2 is a cloned hybrid cell line (B lymphoma x B lymphocyte) which can be induced by bacterial lipopolysaccharide (LPS) to a reduced rate of growth, partial terminal differentiation accompanied by secretion of at least 4 products-IgM, GM-CSF, IL-3, and IL-6. When cells are cloned in the presence of LPS, individual clones are obtained in a wide range of sizes and with many secretory phenotypes. Clones can be obtained that make no products or 1, 2, 3, or 4 products in any combination. None of these phenotypes breeds true. Clones of different size have similar rates of growth. When analyzed by limiting dilution each clone over a 30 fold range of size gives rise to subclones in a wide range of sizes with a similar median in each case. Analysis of clones which are restricted in respect to secreted product show no clone which maintains restriction - most revert to the parental (TH2.2) type following passage in normal growth medium. Most clones are fully sensitive to the inducing effects of LPS when tested shortly after selection and expansion in growth medium. A few clones are found which are resistant to LPS in respect to inhibition of growth, but in most cases this resistance is lost gradually on continued passage in growth medium. One partly resistant line gives rise to resistant and sensitive subclones in growth medium, and these in turn give rise to both sensitive and resistant clones. LPS induces a state of resistance to itself which can be maintained if LPS is added to the growth medium, but which is lost gradually in the absence of LPS. These studies demonstrate an extensive epigenetic regulation of response phenotype in individual cells, and a cellular "memory" of LPS which is partly maintained with cell division.